Conventional metal containers, particularly paint container and the like for use by the consuming public which are cylindrical in shape, typically comprise a container body, a bottom plate closing one end of the container, a ring which is secured to the open end of the container and a lid or a plug which fits into the ring to close the container. Reference may be had to U.S. Pat. No. 4,421,247 to Lombardo et al for a typical example showing the plug and ring construction and the fit therebetween.
The cylindrical container body is usually formed from a rectangular flat piece of sheet metal rolled into a cylinder with the sides joined together by a continuous soldered side seam and a circular bottom plate is then attached, usually by a crimped double seam, to one of the open ends of the cylinder. At the other end of the cylinder, an annular, grooved ring member is similarly attached. Various types of seams can be used and some container are simply drawn or stamped into a one piece container body although the seamed construction described is widely used. To complete the container description, bail lugs or trunnions are crimped into place on diametrically opposite positions on the container. Generally, the trunnions are cup shaped stampings with a peripheral flange formed on the rim of the cup. Typically, the sheet metal, prior to rolling into a cylinder, is stamped by a series of dies to form two indentations which will be diametrically opposite one another after the sheet metal is rolled into a cylinder. The bail lugs are then placed into the indentation and the indentation edges crimped over the bail lug's flanges to secure the lugs to the container body prior to rolling.
Paint containers of the type described have proven acceptable for their intended function and use. There are, however, a number of drawbacks which are principally centered about or arise because of the ring and plug construction described.
From the viewpoint of a can manufacturer, the ring is an unnecessary appendage which, if removed, would materially simplify the container. That is the container could be manufactured with less metal. The container could also be manufactured quicker and more easily because making the ring and then seaming the ring to the container's side wall opening would not be required. Thus, if the ring could be eliminated, the cost of the container would materially decrease.
From the consumer's viewpoint, the ring is undesirable because, despite several patents concepts to the contrary, the ring collects paint and prevents the container from being resealed in an air-tight manner. The ring also inhibits the ability of the user to pour the contents of the container. The ring also prevents all the contents of the container from being emptied.
A less obvious drawback of the plug-ring design is that stacking or nesting of the containers, one on top of the other, cannot occur with conventional designs. Stacking is important from both a shipping and dealer inventory standpoint. Such a feature is simply not readily available with conventional designs because the ring sealing grooves interfere with or prevent the formation of a plug or lid which can function as an interlocking member.
Within the container art, the ring is viewed as a necessary evil which is required to meet the stringent requirements of the paint industry so that, at least initially, an air-tight, shock resistant seal is achieved for the container body. Inherent in the ring-plug seal approach is the elimination of any problems which might otherwise result in attempting to seal, in a repeatable manner, a soldered seam. That is the container is rolled and maintained in a cylindrical shape by a longitudinal soldered seam which extends the entire length of the container. More precisely, each longitudinal end of the container is formed as "U" and the ends are interlocked, crimped and soldered. The soldered seam is thus four times the thickness of the metal. By crimping the ring to the open end of the container and over the soldered seam permits the plug to be sealed within seamless grooves formed in the ring. The ring-plug seal is taught in the container art as being effective because the multiplicity of sealing surfaces. In practice, it is believed that the ring-plug closure initially operates as a seal because i) there is no soldered seam to seal and ii) an interference fit is established between the ring and the plug. That is, as the plug is wedged into the ring, various interference fits are formed by opposing wedge angles between the plug and ring which permanently deform the metal so that the lid is prevented from popping off when the container is dropped. Inherently, the effectiveness of the interference fit is diminished once the plug is removed from and then reapplied to the ring since the metal has already undergone a plastic deformation.
The prior art has long recognized the drawbacks attributed to plug-ring containers, and have developed numerous ringless designs principally to achieve a curled mouth opening in the container for enhanced pourability. U.S. Pat. Nos. 1,419,314 to Sexton and 2,060,504 to Kjellstrom are examples of early ringless paint container designs. Ringless non-paint container designs which are made from plastic, not sheet metal (to which the present invention relates) include U.S. Pat. Nos. 3,056,525 to Deinert and 3,732,909 to Rooke et al and are cited to simply show various locking closures, in plastic, which have certain sealing attributes. A paint container of a conventional sheet metal design which is not entirely dissimilar to that of the parent invention is shown in U.S. Pat. No. 3,333,728 to Burdick. Also, a hybrid design in the sense that a ring is employed with a curled opening is disclosed in U.S. Pat. No. 1,997,291 to Barroll. The Barroll concept, in various forms but always using a ring, is in use today on rectangular or oblong metal containers.
The ringless designs, despite the many claims and assertions made, are not suitable for today's paint containers. For one thing, today's paint containers are dimensionally standardized (within limits). Any newly designed can to be commercially successful must be compatible with existing manufacturing equipment and more importantly, with existing filling facilities. Secondly, the test standards for today's paint containers are stringent. Unique to paint container applications is the force developed within the container at various areas about the inside of the lid from the paint or fluid within the container which acts to pry the lid off when the paint container is dropped or when the container is impacted on its side such as when it enters a labelling machine or a shaker or is otherwise subjected to overall general abuse. In general, the uneven forces act to loosen the lid on the prior art ringless container design and break the air-tight seal which was initially established when the lid was applied to the container. This principally results because there are only two annular seal areas in such designs and this results in an insufficient interference fit when contrasted to that fit established in the ring-plug closure. Additionally, when the lid must snap over a soldered beam which extends to the mouth of the container, the sealing of the container becomes especially difficult. Further, today's paint industry has developed other tests besides the shock test which prior art container designs were not subjected to at the time of their development and which, it is believed, would not be met by such containers today.
In summary of the ringless metal container prior art, it would appear from the art considered that it is recognized that something must be done to rigidize or strengthen the curled bead opening while also providing some mechanisms for removing the lid. Thus, in Ullman U.S. Pat. No. 3,170,590 and Kenny U.S. Pat. No. 1,954,568, the side wall of the containers are rigidized. In Ullman, a bead in the shape of a truncated cone is formed in the side wall and in Kenny a gradually shaped reverse curve is formed in the side wall. Ullman's side wall bead presents an objectionable protrusion whereas Kenny's configuration provides no easy pry for the lid. Burdick U.S. Pat. No. 3,333,728 provides a sharp V-shaped groove in the side wall which rigidizes the mouth while also providing a pry point, and Burdick's container has been commercially used as shoe polish container. The V-shaped protrusion is not acceptable for the paint can application of the present invention since it cannot be easily formed or easily formed without distorting the thickness of the metal. New Zealand Application 170,523 published Nov. 7, 1974 also provides a pry point in a ringless container but, unlike the other prior art cited, uses a mouth configuration which seriously weakens the container.